1. Field of the Invention
The present invention relates to an optical information recording medium in which the state of a recording layer is changed upon irradiation with light, and a change thereof is read as a change in an optical response, thereby achieving recording, erase and reading of information.
2. Description of the Related Art
As one of memory media capable of recording, reproducing and erasing information upon irradiation with laser light, there is known a so-called phase-change type optical information recording medium utilizing transition between a crystal and an amorphous substance or transition between two crystal phases of a crystal 1 and a crystal 2. As this optical information recording medium, for example, CD-RW (Compact Disc-Rewritable), DVD-RW (Digital Versatile Disc-Rewritable), DVD-RAM (Digital Versatile Disc-Random Access Memory) and the like are commercialized.
As a recording layer material which is used in a phase-change recording system, a recording material containing, as a main component, GeSbTe, AgInSbTe, etc. is widely known and put into practical use as a rewritable optical information recording medium.
Also, in recent years, there have been commodified a high-density optical information recording medium which is corresponding to a blue laser wavelength represented by a Blu-ray disc (a registered trademark) and a disc drive apparatus corresponding thereto. As to the high-density optical information recording medium such as Blu-ray disc, in a rewritable type (phase-change type) optical information recording medium, a double-layered disc is put into practical use.
The double-layered disc has a form in which a first information recording layer is formed on a supporting substrate made of a plastic such as a polycarbonate; a second information recording layer is formed on the first information recording layer via an interlayer which is transparent to the wavelength of recording and reproducing laser light; and a light-transmitting protective layer which is transparent to the recording and reproducing wavelength is formed on the second information recording layer.
Laser light which is used for the recording and reproduction is made incident through an object lens from the side of the light-transmitting protective layer. The laser light which has passed through the object lens is condensed into the information recording layer, and the information is recorded and reproduced.
As an example of basic configurations of the information recording layer, there is a configuration in which a metal layer, a transparent dielectric layer, a phase-change material layer, a transparent dielectric layer and a light-transmitting protective layer are disposed in this order from the side of a supporting substrate.
For the purpose of rewriting the information, it is necessary to increase a crystallization rate of the recording material. As a method for increasing the crystallization rate, for example, a crystallization accelerating effect is obtained by bringing a material with poor adhesion properties to a phase-change material into contact with a phase-change material layer (see, for example, JP-A-11-213446 and JP-A-2001-344817).